1. Field of the Invention
The invention relates to a control apparatus for a fuel pump that pumps fuel toward a fuel injection valve of an internal combustion engine.
2. Description of Related Art
Recently, there have been commercialized internal combustion engines for motor vehicles and the like in which fuel is injected directly into combustion chambers to improve fuel economy, etc. In order to inject fuel from a fuel injection valve into a combustion chamber in such an engine despite a high pressure in the combustion chamber, it is necessary to provide a high fuel pressure in the fuel injection valve. In this type of engine, therefore, fuel pumped from a fuel tank by a feed pump is pressurized by a high-pressure fuel pump, and the thus pressurized fuel is delivered to the fuel injection valve. Such high-pressure fuel pumps are described in, for example, Japanese Patent Application Laid-Open Nos. 10-176618 and 10-176619. A construction of a high-pressure fuel pump as described in these laid-open patent applications and the like is shown in FIG. 10.
As shown in FIG. 10, a high-pressure fuel pump 101, as described in the laid-open patent applications and the like, has a plunger 103 reciprocated in a cylinder 102 by rotation of a cam 100, and a pressurizing chamber 104 defined by the cylinder 102 and the plunger 103. Connected to the pressurizing chamber 104 are a suction passage 107 connecting to a feed pump 106 for pumping fuel from a fuel tank 105, a spill passage 108 for leading fuel out of the pressurizing chamber 104 and returning fuel to the fuel tank 105, and a delivery passage 110 for delivering fuel from the pressurizing chamber 104 toward a fuel injection valve 109. The high-pressure fuel pump 101 has a spill valve 111 for establishing and discontinuing communication of the pressurizing chamber 104 with the suction passage 107 and the spill passage 108.
When the spill valve 111 is open and the plunger 103 is moving in such a direction as to increase the capacity of the pressurizing chamber 104 (downward in FIG. 10), that is, during the suction stroke of the high-pressure fuel pump 101, fuel is drawn from the suction passage 107 into the pressurizing chamber 104. When the spill valve is closed while the plunger 103 is moving in the pressurizing chamber capacity-reducing direction (upward in FIG. 10), that is, while the high-pressure fuel pump 101 is in the ejection stroke, the communication of the pressurizing chamber 104 with the suction passage 107 and the spill passage 108 is closed, so that fuel is pumped from the pressurizing chamber 104 toward the fuel injection valve 109 via the delivery passage 110.
Since the high-pressure fuel pump 101 delivers fuel toward the fuel injection valve 109 only when the spill valve 111 remains closed (closed valve period) during the ejection stroke, the amount of fuel delivered toward the fuel injection valve 109 can be adjusted by adjusting the closed valve period of the spill valve 111 through control of the timing of starting to close the spill valve 111. That is, the amount of fuel delivered is increased by elongating the closed valve period of the spill valve 111 through advancement of the timing of starting to close the spill valve 111, and the amount of fuel delivered is reduced by shortening the closed valve period of the spill valve 111 through delay of the timing of starting to close the spill valve 111.
Since the high-pressure fuel pump 101 pressurizes fuel delivered by the feed pump 106, and delivers pressurized fuel toward the fuel injection valve 109, the high-pressure fuel pump 101 allows precise fuel injection even in an internal combustion engine in which fuel is injected directly into a combustion chamber.
When the spill valve 111 is about to be closed during the ejection stroke of the high-pressure fuel pump 101, during which the capacity of the pressurizing chamber 104 reduces, fuel in the pressurizing chamber 104 tends to flow toward the spill passage 108 as well as toward the delivery passage 110. When the spill valve 111 is closed in this situation, the closing movement of the spill valve 111 is accelerated by fuel flowing as described above, so that the impact of closure of the spill valve 111 becomes considerably great. As the impact increases, the operational noise of the spill valve 111 (noise produced by closure of the valve) increases. The operational noise of the spill valve 111 repeatedly occurs every time the spill valve 111 closes.
During normal operation of an internal combustion engine, operational noises of the engine, such as noises caused by combustion of air-fuel mixture and the like, are loud, so that the operational noises of the spill valve 111 continually occurring corresponding to continual closures of the spill valve 111 are not so loud as to annoy an occupant in the vehicle or the like. However, when the engine operational noises become small, for example, during an idling operation of the engine or the like, the continual operational noises of the spill valve 111 become relatively great, so that the annoyance caused by the operational noises become louder than can be ignored.